| OCR Text |
Show 396 DR. J. E. GRAY ON THE GENERA OF TURTLES. [Apr. 1, I. THE TURTLES : with the bones of the vertebree.and ribs expanded and forming in the adult state a complete bony disk, the bones of the sternum separate, but united by dentated sutures into a disk, and edged with a series of marginal bones. Both the back, margin, and sternum are covered with more or less thick, regular, symmetrical, horny plates, as in most other Che-lonians. The head is covered with symmetrical shields ; and the nostrils are in the front, just over the upper edge of the upper beak, which has a more or less deep notch for their reception. This group contains two very distinct families. Fam. 1. CHELONIADCE, Gray, Hand-list Tort. p. 92. The head covered with few, regular, symmetrical shields, and with only one superorbital shield on each side, and two shields on each side of the occiput. The beaks horny, the upper one occupying more than half of the lateral margin, with a sharp dilated margin. The lower jaw fitting into the upper, the lower beak being short, and truncated behind, on a level with the central suture or gonyx, and covered with a large elongate horny plate on each side. The head has in the central line two nasals, a frontal, a parietal, and two occipital plates. Two temporal plates. The cheeks are covered with several plates, three or four forming the back edge of the orbit, the front upper part of which is covered by the outer edge of the nasals. The tympanic cavity in the skull is surrounded by a large smooth concavity, defined by the surface of the temporal bone. The hinder central bone of the dorsal disk, even in the young specimens, reaches to the front edge of the hinder central marginal or caudal bone. Tribe 1. CARETTINA, Gray, I. c. p. 92. The head produced, compressed, and narrow in front. The lower jaw smooth, even on the edge, and covered with the beak on the outside, and only slightly fitting into the upper beak, which is smooth on its inner surface. The alveolar surface of the upper beak and of the skull beneath it with a broad diverging; ridge on the middle of each side, which is separated in the front by a longitudinal groove ; that of the lower beak and jaw deeply concave, with 5. Pl. 31. f. 8. Chelonia tenuis. The figures of these two species do not afford m e the means of determining what species they belong to ; but they are certainly not what I have described as new. 6. Pl. 31. f. 9-11. Euchelys macropus, Philippine Islands, is a young Chelonia, very likely the young of C. mydas or C. marmorata. It is not named on the plate. 7. Pl. 32. Actinemys marmorata, young and adult. Puget's Sound, Oregon, and Sacramento. This species is very different from the Emys nigra of Hallowell, quoted as a synonym in the text, and is evidently a redescription of m y Emys olivacea. |
